1. Field of the Invention
This invention relates to an electrostatic record apparatus such as an electrophotographic printer or copier and in particular to a developing apparatus and an electrostatic record apparatus using a magnetic developer.
2. Description of the Related Art
FIG. 6 is a schematic drawing of an electrophotographic record apparatus using a developing apparatus in a related art. A developing apparatus 4 has two developing rollers 31a and 31b at positions opposed to a photo conductor 1, transport rollers 35a and 35b for transporting a developer 20 to the developing rollers 31a and 31b, and a transport amount regulation member 33 for regulating the transport amount to a predetermined amount. The developing apparatus 4 scrubs and develops an electrostatic latent image uniformly charged by a charger 2 and then exposed to light in a light exposure unit 3 in response to image information and formed on the photoconductor 1 in a developing area 40 in the developer 20 of a mixture of toner 21 and carrier 25 on the developing roller 31.
Next, an electric field in the move direction of the toner 21 to a record medium 8 is formed by a transfer unit 7 and the toner 21 on the photoconductor 1 is transferred to the record medium 8. When the record medium 8 on which the toner 21 is deposited passes through a fuser 9, it is heated and pressurized and the toner 21 is fused and fixed onto the record medium 8. The remaining toner 21 or adherents of paper powder, etc., on the photoconductor 1 after transfer part passage are separated and removed from the photoconductor 1 by a cleaning unit 11 and are collected.
Next, the operation of the developing apparatus 4 will be discussed with FIG. 5. In the developing apparatus 4, the two developing rollers 31a and 31b each comprising a rotatable sleeve roller 32 (32a, 32b) on the outer periphery of a fixed magnet 30 (30a, 30b) are opposed to each other with the transport amount regulation member 33 between. In the developing roller 31a, the sleeve roller 32a rotates clockwise in FIG. 5, namely, in a direction in which the developer 20 moves in the opposite direction to the move direction of the photoconductor 1 in a developing area 40a (reverse rotation).
In the developing roller 31b, the sleeve roller 32brotates counterclockwise in FIG. 5, namely, in a direction in which the developer 20 moves in the same direction as the move direction of the photoconductor 1 in a developing area 40b (forward rotation).
The developer 20 agitated by an agitation section (not shown) and transported to the proximity of the developing roller 31bis magnetically attracted to the surface of the sleeve roller 32b by the magnetic force of an N1 pole of the magnet 30b in the developing roller 31b, and as the sleeve roller 32b rotates, the developer 20 is transported to an S1 pole.
The transport amount regulation member 33 is placed with the spacing adjusted between a transport amount regulation part 34b and the sleeve roller 32b. The transport amount of the transported developer 20 is regulated according to the spacing between the transport amount regulation part 34b and the sleeve roller 32b, which will be hereinafter referred to as doctor gap, as the sleeve roller 32b rotates, and a given amount of the developer 20 passing through the transport amount regulation part 34b arrives at the developing area 40b. 
The developer 20 whose transport amount is regulated according to the doctor gap is transported from the S1 pole to an N2 pole further as the sleeve roller 32b rotates, and forms a magnetic brush by a magnetic field produced by the N2 pole and its surrounding pole in the developing area 40b and scrubs the photoconductor 1. The doctor gap is set so that the transport amount of the developer 20 becomes a proper value relative to the spacing between the photoconductor 1 and the sleeve roller 32, which will be hereinafter referred to as developing gap, so that the developer 20 does not disorder the developed image by excessively scrubbing the photoconductor 1 or so that sufficient print density can be provided because of sufficient transport amount relative to the developing gap.
The developer 20 that cannot pass through the transport amount regulation part 34b gets over the transport amount regulation member 33, is transported to the developing roller 31a, and is regulated so that the transport amount of the developer 20 becomes constant according to the spacing between a transport amount regulation part 34a and the sleeve roller 32a. The developer 20 passing through the transport amount regulation part 34a is transported to the developing area 40a. 
The developer 20 that cannot pass through the transport amount regulation part 34a either is returned to the agitation part by a scraper. The developer 20 transported to the developing area 40b by the sleeve roller 32b and completing the developing is transported with rotation of the sleeve roller 32b and is returned to the transport roller 35a. 
The developer 20 transported to the developing area 40a by the sleeve roller 32a and completing the developing is transported with rotation of the sleeve roller 32a and is returned to the agitation part by the scraper.
Thus, the developing apparatus of the type wherein the two developing rollers are opposed to each other with the transport amount regulation member 33 between and transport the developer in the opposite directions is called center feed type developing machine. The configuration wherein three or four rollers are included rather than the configuration wherein only two rollers are included as in the example is also available.
It is necessary to develop a developing system which is capable of performing high-density print in an electrophotographic record apparatus for printing according to the process as described above and provides high resolution and is small at low cost with no carrier deposition.
In the developing apparatus, toner is deposited on an electrostatic latent image formed on the photoconductor, whereby the latent image needs to be developed with good reproducibility. The amount of the developer transported to the developing area is an important factor to provide the optimum image quality. To faithfully reproduce the latent image in the developing apparatus using a dual-component developer, the case increases where the developing gap is set narrow to 0.6 mm or less and the developer amount to be transported is also set small so as to eliminate defective conditions of scraping, etc., occurring because the developer amount is too much.
However, to transport a proper amount of the developer to the narrow developing gap, the doctor gap needs also to be set narrow in response to the developing gap, and must be made a very narrow gap of 0.4 mm or less in some cases.
To develop in a narrow developing gap, if the amount of the developer transported to the developing area varies, a defective condition on the image quality such as inconsistencies in density easily occurs. It is difficult to set such a narrow doctor gap over all area in the developing roller shaft direction with good accuracy. Particularly to use a 400 mm or more long developing roller to perform wide print or to use a small-diameter roller to miniaturize the developing apparatus, a problem of a different transport amount from one location on the roller to another easily occurs.
Variations in dimensions of the developing roller, the transport amount regulation member, etc., because of a manufacturing error cannot be avoided and it takes much time in adjustment at the assembling time. Moreover, the transport amount of even the developing roller set in the appropriate range by adjustment changes with abrasion of the sleeve roller surface and thus if the roller formed on the surface with asperities by shot blast or metal shot for enhancing the transport capability is worn by secular changes, a problem of changing the transport amount and degrading the image quality easily occurs.
The center feed type developing machine has a pair of rollers different in photoconductor scrubbing direction in the developer and thus has the advantage that defective conditions of chips, etc., in the image end parts by scrubbing on the rollers cancel each other out and the developing machine can perform print of high image quality with less chips of the image end parts. When the transport amount regulation member positioned in the gap between both rollers regulates the amount of the developer transported to the developing areas of both rollers, both developing rollers are placed close to each other and thus developer transport to the transport amount regulation member or the regulation state varies more easily because of a manufacturing error or a fix position error of the developing rollers or the transport amount regulation member as compared with a developing apparatus using one developing roller; this is a problem. Higher assembling accuracy of the developing apparatus than that of the usual developing apparatus is required.